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Air radiation dose rate

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 Air radiation dose rate measured at the monitoring station is the physical quantity of air absorbed dose rate by the gamma ray(Gy/h: Gray per hour). Air absorbed dose (Gy: Gray) is defined as the quantity of the energy (J: Joule) that gained when 1 kg of air catches the radiation. As the strength of the radiation can be expressed as a quantity of energy received in a certain time, quantity of the energy received from radiation in an hour (Gy/h) is defined as the strength of the radiation.

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 Monitoring station observes the air radiation dose rate (Gy/h) measured as the physical quantity, and it is shown as the value converted to the dose equivalent rate (Sy/h: Sievert per hour) that expresses how it affects the human body.
 This site shows the value converted as 1[μGy/h] (Microgray per hour) = 1[μSv/h] Sievert per hour) , according to the Environmental Radiation Monitoring Guideline (former Nuclear Safety Commission)
 Dose equivalent (Sy: Sievert) is an indicator that assumes influence that a radiation gives in the human body as a standard, and officially, it is calculated by multiplying the coefficient corresponding to the radiation type or the organization of human body where received radiation, based on absorbed dose (Gy: Gray) measured for physical quantity

How to measure the air radiation dose

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  • Low dose detector (NaI scintillation detector)
     It measures the dose rate using a phenomenon that a radiation (gamma ray) emits light when it hits a crystal of NaI, and can measure correctly as low as a few nano Gy/h(10-9Gy/h)
     On the other hand, when the air radiation dose increases, it cannot measure correctly as it cannot count too much number of the emission. Therefore the maximum measurable value is defined as a several micro Gy/h (10-6 Gy/h)

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  • High dose detector (ionization chamber)
     It measures the dose rate using a phenomenon that a radiation ionizes (that is, divides into an ion and an electron) when it hits gas, and can measure as high as 100mGy/h(10-1Gy/h).

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